8 BRITISH FOSSILS. 



evidently follows that the ink-sac is not in its natural place, since it 

 occupies that of the septa, which would be impossible.* 



" M. Quenstedt has just published, in Leonhard and Bronn's Jahr- 

 buch, a memoir, the intention of which is to prove that the Belopeltes 

 do not belong to Belemnites. He gives, in this memoir, the figure of a 

 Belopeltis, which does not appear to me to be exact, because it repre- 

 sents the fracture which is always observed at the posterior part of 

 these fossils, not as a fracture, but as the commencement of the shell ; 

 this would then be the point from which the successive growths Avhich 

 formed the shell started. M. Quenstedt had the goodness, in August 

 1839, to show me, in the museum of the University of Tiibiugen, the 

 original of this figure, but I was unable to agree with him on this 

 point. The striae of growth of this fossil present no point that can be 

 considered as the origin of the shell ; the asymptotes and the hyperbolic 

 striae can be very well observed cutting transversely the lines which 

 this naturalist takes for the origin of the shell ; therefore the part of 

 the shell whence its growth emanated, was inevitably situated beyond 

 that line. The origin must have been at the point of union of the two 

 asymptotes, and the shell is necessarily incomplete at its extremity. 

 Now the whole theory of M. Quenstedt is based on this obviously 

 erroneous mode of interpreting the fossil, so that it cannot be ad- 

 mitted." 



In 1842, M. D'Orbigny, Paleontologie Francaise, Tome ler, p. 41, 

 and Planches II., III., IV., described with much confidence, and 

 figured, what he terms the " osselet corne " of the Belemnites. 



"It varies but little in form, as I have been enabled to judge by the 

 examination of more than 15 distinct species, the rostra of which 

 are very different, while I have always found it to have the same 

 configuration. It is composed, in front, of a broad spatuliform plate, 

 exhibiting, in the middle, a wide dorsal regionf (a, Fig. 1, PI. IV., et 3, 

 PI. III., the part comprised between the lines b, 4), the angle of which 

 always exceeds ten degrees, covered with ogive-like striae of growth, 

 Avhich unite on each side at the metlian line, which is sometimes 

 projecting or slightly grooved. 



" On each side of the dorsal region are the lateral expansions,^ Avhich 

 pass from this region and form, on each side, delicate horny plates, 

 which are marked with lines of growth passing obliquely from above 

 downwards, and from the dorsal to the ventral face. These expansions 

 accompany the " osselet " through its whole length (see PI. III., fig. 2, 

 PI. IV., fig. 1, the parts which lie between the lines c, d), and diminish 

 in width from above downwards as far as the inferior part, where they 

 form a longer or shorter conical cup, which appears to constitute about 

 a third of the whole length. On the sides, at the point of junction of 

 the lateral expansions with the terminal cup, the lines of growth 

 suddenly become sinuated, form curves with a dowinvard convexity, 

 and become transverse in the whole ventral region, to give rise to the 

 terminal cup, a kind of reversed horny cone, in which the chambers are 

 developed successively as the animal grows." 



It appears, however, (see p. 43 of the work cited) that all this elabo- 

 rate description of the " osselet corne " is not based upon the exami- 



* It would be interesting to know -what the striae seen upon the counterpart by 

 Professor Agassiz really were, and why Dr. Buckland nowhere says anything about 

 them. I suspect that they were the conothecal striae. 



f The Asymptotes of M. Voltz's Memoir, p. 3. 



J It is these lines, convex when the cone is reversed, which form what M. Yoltz 

 calls " hyperbolic regions." 



